1. Field
The present invention relates to a photoelectric conversion device, an imaging device, a method for manufacturing an imaging device and an imaging apparatus.
2. Description of the Related Art
JP-A-2007-88033 discloses an organic photoelectric conversion device having a pair of electrodes and an organic compound-containing photoelectric conversion layer provided between the electrodes. The photoelectric conversion layer as referred to herein means a layer which receives light to generate a charge corresponding to the amount of received light. Also, JP-A-2009-147147 discloses an imaging device using such an organic photoelectric conversion device. Since performances such as high sensitivity and low dark current are required in the imaging device, high sensitivity and low dark current are also required as performances in the organic photoelectric conversion device.
In order to enhance the sensitivity, an enhancement of light absorption, an enhancement of exciton dissociation efficiency and an enhancement of transport properties of dissociated charges are necessary, respectively as performances of the photoelectric conversion layer. In general, in a photoelectric conversion layer of an organic solar cell, a technique for promoting the exciton dissociation on a junction surface between a p-type material and an n-type material is adopted. In particular, as a technique for increasing an junction area between the p-type material and the n-type material while ensuring a path of the dissociated charge, there is often adopted a technique for forming a layer (bulk hetero layer) having a p-type material and an n-type material mixed therein. However, when a photoelectric conversion material or a bulk hetero layer which is used in a photoelectric conversion layer in organic thin film solar cells or the like is applied to an imaging device as it is, in many cases, the dark current becomes large. It may be considered that this is related to a thermally excited carrier from HOMO of the p-type material to LUMO of the n-type material, and it may be considered that this is caused due to the matter that the carrier flows into an electrode due to an electric field impressed to the photoelectric conversion layer or existing in the inside of the photoelectric conversion layer.
Such a dark current in the organic photoelectric conversion device is caused due to a dark current by a charge to be injected from the electrode into the photoelectric conversion layer, a dark current by a free carrier upwelled in the photoelectric conversion layer, a current due to a physical short circuit such as partial leakage. As a countermeasure to the dark current to be injected from the electrode, there is a technology for inserting a charge blocking layer between the electrode and the photoelectric conversion layer. Also, as a countermeasure to the leakage, there is reduction of irregularities of the electrode, removal of dusts attached to a substrate, or the like. However, a method for effectively suppressing the dark current by the free carrier upwelled in the photoelectric conversion layer has not been known yet.
In an inorganic material, it is broadly known that a dangling bond becomes defective, so that it may become a carrier generation source. For example, JP-A-2009-54794 describes a possibility that with respect to an SiOx layer functioning as a hole blocking layer contained in the organic photoelectric conversion device, its defect becomes a carrier generation source.
JP-A-2008-115460 and JP-A-2004-363577 disclose that there is a correlation between a defect (dangling bond) in a photoelectric conversion layer (photoactive layer) in an inorganic solar cell and an electron spin density.
However, all of JP-A-2009-54794, JP-A-2008-115460 and JP-A-2004-363577 show a thought that there is a correlation between a defect (dangling bond) in an inorganic material layer and an electron spin density, but they do not consider how to suppress a free carrier which will possibly become a dark current source in a photoelectric conversion layer where a dangling bond does not exist (specifically, an organic material-containing photoelectric conversion layer).